<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
  <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
</head>

<body>
  <div id="app">
    <input type="text" v-model="title" />
    字数： {{ word }}
  </div>
  <script>
    Vue.config.productionTip = false;

    const vm = new Vue({
      el: "#app",
      data () {
        return {
          title: "",
          count: 2,
        };
      },
      computed: {
        word () {
          return this.title.length;
        },
      },
      watch: {
        title (newVal, oldVal) {
          console.log("请求数据", "新:" + newVal, "旧:" + oldVal);
        },
      },
    });
  </script>
</body>

</html>